1. Field of the Invention
The present invention relates to an intake throttle valve apparatus for an internal combustion engine. More particularly, the present invention is concerned with an intake throttle valve apparatus whose valve element is rotated by a driving motor through a reduction gear mechanism in response to actuation or depression of an accelerator pedal.
2. Description of Related Art
Heretofore, such an intake throttle valve apparatus is known that the opening degree defined by a valve element of a throttle valve incorporated in the intake throttle valve apparatus is controlled by means of a driving motor through a reduction gear mechanism in response to manipulation or depression of the accelerator pedal.
In the hitherto known or conventional intake throttle valve apparatus mentioned above, torque generated by the driving motor is transmitted to a valve shaft supporting the valve element of the throttle valve through a reduction gear mechanism or train which includes an output gear fixedly mounted on a motor shaft of the driving motor, an intermediate gear meshing with the output gear and an input gear fixedly mounted on the valve shaft and meshing with the intermediate gear with a view to increasing the torque to a magnitude required for controlling the opening degree of the throttle valve. The reduction ratio of the reduction gear train is substantially “10” or more. For more particulars, reference may have to be made to Japanese Patent Application Laid-Open Publication No. 266666/2002 (JP-A-2002-266666).
The hitherto known or conventional intake throttle valve apparatus mentioned above however suffers a problem that the intermediate gear and a gear pin for supporting the intermediate gear are required for the torque transmission because the reduction gear train is implemented in a so-called two-stage speed reduction structure including the intermediate gear, and thus the number of constituent parts of the intake throttle valve apparatus increases correspondingly.
Moreover, in the conventional intake throttle valve apparatus, a relatively large inter-shaft or inter-axis distance is required between the output gear and the input gear because of interposition of the intermediate gear. Consequently, the size or dimension of the intake throttle valve apparatus is necessarily determined by the inter-axis distance and thus difficulty is encountered in implementing the intake throttle valve apparatus in a small size, giving rise to an additional problem. This problem becomes more remarkable from the standpoint of layout when the intake throttle valve apparatus is installed in a compact type gasoline engine car of cylinder volume of 1.0 liter or less. For coping with this problem, it may unwantedly become unavoidable to change or modify the specifications of the engine body as well as peripheral equipment, presenting a further problem.